The present invention relates generally to a displaying apparatus for a vehicle. More particularly, the present invention relates to a displaying apparatus for a vehicle wherein a displaying device is disposed on the rear surface side of a semitransparent reflecting member for displaying items such as a vehicle speed, an engine speed or the like, the reflecting surface of the reflecting member being oriented toward a driver who visually observes the foregoing items with his eyes, and a reflective mirror is disposed at the position located opposite to the displaying device while the semitransparent reflecting member is interposed therebetween.
A displaying apparatus of the foregoing type as illustrated in FIGS. 3 and 4 has been hitherto used. In the drawings, reference numeral 1 designates a case which is accommodated in an instrument panel. A half mirror 2 serving as a semitransparent reflecting member is arranged in the case 1 with such an attitude that a reflecting surface 2a of the half mirror 2 is oriented toward an eye point E of a driver who visually observes items appearing on the reflecting surface 2a of the half mirror 2. A display device 3 for displaying various items such as a vehicle speed, an engine speed or the like is disposed on the rear surface side of the half mirror 2, and a concave mirror 4 is disposed at the position located opposite to the displaying device 3 while the half mirror 2 is interposed therebetween. In addition, a front glass 5 molded of a transparent material such as an acrylic resin or the like is fitted to the case 1 so as to protect an opening portion la of the case 1 from damage, injury or the like by closing the opening portion 1a with the front glass 5.
In FIG. 3, reference numeral 6 designates a meter hood molded integral with the instrument panel, and reference numeral 7 designates a warning displaying unit. Items appearing on the warning displaying unit 7 can visually be recognized by driver's eyes through the front glass 5. The displaying device 3 is disposed at the position where its displaying surface is located substantially at a focus of the concave mirror 4 in order to assure that the items appearing on the displaying surface of the displaying device 3 are visually observed on the reflecting surface 2a of the half mirror 2 in an enlarged scale by driver's eyes.
Displaying light emitted from the displaying device 3 permeates through the half mirror 2 to reach the concave mirror 4 which in turn reflects the displaying light toward the half mirror 2. Subsequently, the displaying light deflected at the reflecting surface 2a of the half mirror 2 is irradiated toward the driver's eye point E so that virtual images corresponding to items on the displaying surface of the displaying device 3 are visually recognized by drivers's eyes within the displaying range of the reflecting surface 2a of the half mirror 2 when a driver visually observes the reflecting surface 2a of the half mirror 2 with his eyes. At this time, the items appearing on the reflecting surface 2a of the half mirror 2 can visually be recognized by driver's eyes from a remote location in an enlarged scale with the aid of the concave mirror 4 and the half mirror 2 both of which serve to repeatedly reflect displaying light while exhibiting an enlarging activity.
With the displaying apparatus constructed in the above-described manner, however, when exterior light is irradiated to the displaying apparatus from the eye point E side, there arises a problem that the exterior light permeates through the front glass 5 and reaches the half mirror 2, and subsequently, it is sequentially reflected via the half mirror 2, the concave mirror 4 and the half mirror 2 to return to the driver's eye point E as shown in FIG. 5, causing driver's visual observation to be disturbed by the exterior light.
To cope with the foregoing problem, a measure of reducing permeability of the front glass 5 has been hitherto taken for the purpose of preventing driver's visual observation from being disturbed by exterior light. However, in case that the front glass 5 has flat spectroscopic properties and the permeability of the front glass 5 is reduced at an average rate for all wavelengths of the exterior light, there arises another problem that brightness of each virtual image to be visually recognized by driver' eyes can not sufficiently be maintained with the displaying apparatus.